Clutch spring



Patented Sept. 5, 1950 William Carleton "Starkey,

Indianapolis, and

liarnilton' ll. McCormick,-Carmel, Ind., assignms to Fletcher Trust Company, Indianapolis,

Ind., a-corporation, as trustee Application December 5, 1945,Serial No. 632,986

11 Claims. '1

This invention relates to a clutch element of the coiled wire type for use in a frictionclutch of the kind'usuallyreferred 'to'as a spring clutch.

The principal objects are to provide an improved shape of wire stock for making coiled clutch springs and, 'as-an article of manufacture, an improved friction clutch element of the coiled wire'type.

Specific-objects include the making of clutch spring wire stock of such cross sectional shape that (a) it. canbs rolled-or drawn in high quan tity production with a practical-minimum o'f destructive wear and strain on the necessary dies or tools, (13) it will, when coiled by the-usual methods, result in a clutch "spring having its principal "masses so distributed as --practically ideally to resist the complicated strains and shocks incident to service as a clutch spring, Whether designed to expand-to-clut'ch or -con-' tract+'tc-clutch, and (c) "the resulting-coil may be finished, as by simple centerless *or center grinding, to remove scale and surf ace-irregularities while providing (economically from "the standpoint'of manufacturing-cost) iclutching land areas er appropriate "and controllable extent axially of the coils, having regard sparticularly to thespecial service to be arendered by respec tively "different portions of :the clutching land surface 'as will the later explained more :iully herein although" well known in the art.

The spring -stock:hereby= disclosed :asdrawn *or rolled QFig-Z'later described), has,-incross section, a rprincipal oI' longitudinal :medial plane DiD-estab1ishing a main dimension; :a :transverselplane C--C establishing ashorter zorlminor dimension; the bulkcofathestock is :disposed symmetrically about the principal plane and-.cn :the side of th'e'transverseplanezwhich is to become thGIlGIl-ClutGhirrg peripheral ,portion .of the coil in ithefinished spring, and -a lesser amount or portion:ofsstoclron the :oppositesideoi the transversewshorrten dimensionpla-ne and symmetrically distributedvabcut thgprincipal plane. The? lesser bulk clutching portion-with the shorter-dimension' as awbase, is preferably, roughly of regular ttrapezoidalsshape and with-sides convergingiaway .from-the baselat :a comparatively wide included angle (e. ;g.--6()- degrees) joined byraacrown portion which, in the rolled or: drawn stock,zis preterably a regularly :curved surf ace formed ion :01 defined by lazradius having its :center located within the trapezoidal area and-along'ithe principalrplan'e, sovthat the curve. isttangenttothe'convergingsides. The curvedsurfaceuportion'is circularly-(e. :g. cylindrically) finished-to .iorm' .the

clutching face of the spring :and, if generated'a's indicated, it and the converging sides are easy to'formby dies or-rolls (no'abrupt deviations or sharp corners) to present to the land-forming grinding or finishing'tools a region'whic hywithin practical limits (allowing for production manufacturing tolerances) mayibe finished with controlled narrow width at one end-of thenspring (energizing end) and to increase :gradiently in width (or abruptly-if desired) #toward the opposite or load carrying end of the spring. Thus the energizer or teaser coil 1 or coils has :or have narrow clutching land surface portions for cutting through obstinate oil films -'(as :at sub-zero temperatures) and the balanceof the 'coilshave, ormay havaas .willbe presentlyexplained; grad ual'ly increasing width-to withstand the :grad ually "but rapidly increased :pressures from coil tozcoil incident :to efficient clutchspring use as is wellknowninthe art. concomitantly; by provision :of the converging sides mentioned, V- shaped grooves are formed which decrease in depthan-d :cross sectional area-"from the energizing end or spring portion where large'lubricantreception spaces are desirable, toward the load carrying end :or' toward the region of the-clutch where. itbecomes increasingly A desirable to retain lubricant between the coacting clutch surfaces'in order'to prevent galling or scoring.

The non-clutching portion of the :drawn :0! rolled stock, at the side opposite the transverse orshort dimension plane mentioned, is also preferably roughly of regular'trapezoidal form' 'being not known slight-wedge or keystone shape so thatas-the .stock'is coded the portion which becomes :subjected mainly to compressive strain (toward the coil axis) increases in width (axially of thecoil) and the :opposite side which is subjected mainly to tensional strain decreases in width. Additionally, partly 'to avoid sudden change in direction on part .of the wireeforming die or roll surfaces--henceto minimize-wear and strainon the tools and thereby produce smoother spring surf aces-the paired slightly converging sides of l the stock, merge in generous acurves into thesconnec-ting side which later'loe'comes orestablishes the non-clutching .peripheral "face of thezflnishedspring. -Inthefinished springmetal flow dueprincipally to the compressive strains and: heat generated-by coiling of .the stoekrtends to eliminate "the curves and will eliminate .them if :properly proportioned in relation "to thestock section as a-whole.

In -:a spring which is designed to contract in clutching (not shown) the slightly-.convergingpr keystone-face sides would, obviously, converge toward the clutching faces rather than away therefrom as in the illustrated embodiment.

In order to produce finished (e. g. ground) clutching lands which increase gradiently in width in a direction from the energizing toward the load-carrying end of the spring either of two methods or appropriate variations thereof can be used. For illustration, in the case of an expanding-to-clutch type of spring the stock can be partly or wholly taper-wound; then expanded on a cylindrical mandrel leaving the clutching surface region exposed, and that surface then subjected to cylindrical grinding. When the spring is removed from the mandrel its restored normal shape results in provision of larger teaser coil diameters with narrow lands, effective to remain engaged during overrun of the clutch with the coacting clutch surface, and gradiently increasing widths of land and smaller diameters at or toward the load carrying coils which would be finished normally to fit or slightly clear the coacting clutch surface, as desired. The other method, which is the reverse of the above, is to form the coils cylindrically; then expand the coiled blank onto a tapered or flared mandrel and then to grind the clutching periphery cylindrically. When the mandrel is removed the spring assumes its original shape, and has wide lands and relatively smaller diameters at or toward the load carrying end and narrowing lands and increasing diameters at or toward the energizer or teaser end. Usually the difference in diameter on part of the difl'erent portions of the mandrel (or of the different coils if taper-wound) is on the order of a few thousandths of an inch, wherefore the radially somewhat thicker energizer coils are nevertheless adequately fiexible.

If the clutch spring is of the contracting-toclutch type it would, if coiled as a cylinder, be contracted into a tubular (e. g. flared or slightly tapered) mandrel and ground on its inside face; the more contracted, hence eventually larger diameter, coils being ground off to a greater extent as would be appropriate for service as loadcarrying coils in that type of clutch. The above 1discussion indicates further objects of the invenion.

A further important object is to provide a form of stock material so contoured in its cross sectional configuration that when wrapped into its helical form to its preset radius it will provide a spring clutch which can be so wound as to be approximately solid from end to end considered axially and approximately solid from its mean or pitch diameter to its non-clutching surface considered radially, which will provide the desired lubricant receiving and retaining channels in its clutch surface and in which its predetermined width of land will be controllable under practical production conditions wherein, as usual, the spring stock is ground to fit its companion diameter and for removal of scale and surface irregularities, and wherein the increase in land width imposed by such grinding is at a much less rate than is the rate of grinding of the surfaces.

Various other objects and advantages of the invention will be in part obvious from an inspection of the accompanying drawings and in part will be more fully set forth in the following particular description of one form of device embodying the invention, and the invention also consists in certain new and novel features of construction and combination of parts hereinafter set forth and claimed.

In the accompanying drawings:

Fig. 1 is a view partly in axial section and partly in side elevation of a spring clutch constituting a preferred embodiment of the invention;

Fig. 2 is an enlarged cross sectional view showing in full lines the outline of the wire stock from which the coils of Fig. 1 are eventually formed and showing certain of its relative dimensions.

Figs. 3 and 4 are each enlarged cross sectional views of any two of the adjacent coils of Fig. 1; Fig. 3 showing in full lines the configuration developed from that of Fig. 2 when the stock is wound into its cylindrical form before grinding; Fig. 4 showing the cross section of the finished and ground form of coil shown in Fig. 1; and

Fig. 5 is a schematic comparative illustration plotted to indicate the relative measurements in grinding the wound coil spring to the desired diameter and to the final width of land.

There has been selected for specific discussion a clutch 10, Fig. 1, which comprises an outer member H provided with a cylindrical bore defining a clutch surface I3, in which bore is fitted an externally gripping or expanding type clutch spring M. The clutch spring is wound to provide a series of abutting coils l2 and has its outer perimeter ground to provide a clutching land surface l6 of proper diameter to operate within the bore l3, different portions of the spring preferably having different fitting or cooperating relationships to the bore.

The main body of the spring comprises at one end a large number of coils, which may be referred to as the load carrying coils, indicated by the group included in the bracket A and at the other end comprises one or more exciter or energizer coils grouped within the bracket B. In grinding the coils to their requisite diameters the coils embraced by the bracket B are ground slightly oversize compared to the diameter of the coils grouped within the bracket A.

In forming any particular spring coil that size of stock material is selected which will best respond to the required size of clutch desired, giving due consideration to the work for which the clutch is intended as above outlined. Referring to one representative specimen of this stock material as shown in Fig. 2 (expanding-to-clutch type) it will be noted that, as drawn or rolled, it is generally of bi-symmetrical polygonal form in cross section, having five fiat sides and a curved side I! which in the finished spring is usually desired to be ground straight to form the peripheral clutch surface or land. The stock material as drawn or rolled has its greatest width (minor dimension discussed above) indicated by the line CC nearer to the side (top) which is to form the clutching surface or land than it is to the opposite or non-clutching (bottom) side l8, so that as much material as practically possible is, in the finished spring, massed between the line CC and the non-clutching side. As viewed in Fig. 2 the cross section is symmetrical about a medial vertical line D-D (principal plane) which bisects the sides I '!-|8. From this line 0-0 the width is gradually reduced both upwardly and downwardly as viewed in Fig. 2 so that the opposite pairs of sides converge towards the medial line DD. The opposite long paired sides l920 (see Fig. 2) converge slightly towards each other and merge into the side I8 in generous identical curves 2|. The sides l9 and 20 are almost but not quite parallel to the medial line. D-D. In actual. practiceas. previously outlined,.the angle of. divergence. of. the sides, I19 and 20 is selected to. bring. these sides almost if. not. entirely into. exact parallelism so. that in. the final wrapped torm,.see. Fig. 3,.tne resulting, sides 19' and 20 of adjacent coilsmay contact in a. face, to face relation overa material. area and substantially from tha-l'ineC-C'to the finalnonclutching-surface Hi". In the-illustratedinstance the anglev formed between each sidel'fi. or 211.- and a perpendicular to the adjacent end of theline C,-C. is aboutthree. degrees. H v

The opposite paired relatively.- short. sides 2?, and 23. which lead to tqeendj which. is. to. form the clutch. surface converge. from. the. line. C--C to the medial. line D-D and. each side tormsan angle of about sixty degrees. with the line -4;. Thus if the lines 22. and 23 were extended. they would. form an included angle. of. sixty degrees. These sides and 23', in the illustrated. form, are tangent toa relatively short. arc. of a. circle forming. or defining. the. curved side I! which is to be ground. as hereinafter. described Many springs: which have. functioned. satisfactorily under conditions herein described have been found to possess. approximately the. same relative dimensions. In. these several cases the height of. cross section of material in. eachcoil as measured along the medial: line.D---Q Fig.- 2 will be referred tov as. the distance it whichd-istance is used. herein to provide. a basis for comparison with the other dimensions of the cross section; The line (3-0 which defines themaximuinz width has a length aboutseventy per center the-height h sov that the cross. section has: greater depth along the line l'J- -D than the width, measured along, the line C -C. This line C.--C is; located nearer the crownportion. of theend it than the surface l8. so that the bulk of material lies between the. line-C and the side 18. In the form illustrated the distance between. the line CC and. the crown ofv the end i1 is about forty per cent-of. the. distance 71... The diameter of. the circlewhose arcmay form thecurve H. is about twenty per cent of the distance it so that its center is beyond. the line. C---(-J.fr0mside 18.. The external diameter of the coils bracketed. by A, and which is also the internal diameteroi the bore 43 with which they are designed. tov coact as: a clutchis-approximately nine and. one-half times the distance In I The stock wire of. the peculiar cross sectional form. above described and illustrated in Fig. 2 is wound into a spiral coil following conventional practices in this respect. winding each coil takes the form shown in cross section in Fig. 3. Comparing theshowing; in Fig. 2 with, that in Fig. 3 it is seen that the width along. the base side I8 has broadened. slightly to a new width It, so. that the area-bounded. by the sides 2 3,, I8". I 9' and the 1ine.C-C forms a rec.- tangular shape more closely approaching a square than when in the initial form shown in Fig. 2.

Considering. the cross section above the line 0-6 it will be found that it is of somewhat narrower width than its original Fig. 2 form and incidentally somewhat flatter. In Fig. 3 the arc ll morenearly approaches a fiat surface asindi- As. the result of. this w cated at 24 and thus more nearly approaching the final fiat ground surface or land indicated by the dotted line 25 in Fig. 3 and full line in Fig. 4. Incidentally this wrapping operation reduces the curvature of the rounded edges 21 so that in the final form the inner perimeter of the clutch spring: is continuous from end to end except for. the. presence 012a spiral channel 26. of extremely smallcrosssectionandwhichirom an ideal. standpoint. should be nonrexistent.

Considering Rig, 4; then. it. can. be. assumed that.

the portion. below. the line (ls-C. is rectangular and the part above. the line. Cs-C forms. the. frustum ot a regular trapezoid. in cross section. Itis appreciated that in. arrivingatthe dimensions for. the. stock. wireshown. in. Fig; the operation was worked backwards; starting. with the desired final:- configuration. shown inFig. 4: and.

figuring the distortions. which-would. develop, in.

of the stock materialshownin'l 'ig. 2 duecon sideration was. given towhat? was to become the final overall radial dimensions oizth'ei'spring inits relation to the diameter of the boreizz and the w-idtli' oi. the lin'e ifia Inv general. this means that in winding the stock: springs into theforin; shown in cross sectionin. Fig 3 the diarn'etenof the winding should he slightly'oversize so that when ground downto the proper finalv diameter as demonstrated Icy-Fig. 4'- the preset dimensions of' the land's-2 5 will beappropriatefor clutching;

In Fig. 4 the upper portionof the wire section is laid out upon avertical scale inthousandths of an inch to" indicate the extent of grinding of' its cl'utchsurface. The horizontally arranged scale, in thousandths of: an inch, isindieative of the width of the land resulting from the grinding to diameter. Considerin successive unit. distances alongithevertical ordinate of the chart and comparing. such distances with sueceeding widths of lands it will be seen that while grinding inwardly. succeeding unit distances. in creases. the widths of the lands, each succeed ing increment of. increased. width is less than said unit. distance 01 depth. of grinding For example, if. the spring, is. to be grounds to. vary diameter by .010 of. an-ihcheach section. of. spring. as. shown. in. Fig; 5-, will. be ground. .005. of. an inch which.williform a landfills having. width. of .035. Varying. the: diameter or. the sprin another .910 (grinding. such. section. .095). would. increasethewidth. of. the land. to. .(l lB. An additional .010 relief: would. increase the land to .058 and further .010 relief would increase it to .064.

Width ot the. land, will, therefore, be maintained at a minimumot variation during the grinding operation. As: compared with a wire havinqthe usual curved; or. arcuatecross section indicated: by dotted lines atXL,.the width of the land of: the above described. section increases or varies much less rapidly with: the grindingof the clutch? surface. Thus, a secticrr has is en developed which: lends itself 60 more ready coir- ,rol of the width of thefland in surfacegrinding of the spring: to size: Thisshas the advan tage of permitting the same wire: to'be'wound into a spring clutch having a wide rangeof clutch surface diameters; and" whereinthe processing of: the spring will permit oisuhstantiai variations of diameter in. the. grinding. op-

7 eration, even in a single spring, while holding the land width within prescribed tolerances.

As previously explained, in winding the clutch spring, or preparing the spring for grinding, different coils will usually vary somewhat from each other in diameter, so that in grinding the clutch surface there will be an automatically established deeper grind on some coils than on others (e. g. coils A in comparison to coils B, Fig. 1). By means of the form of spring section herein explained, such variations in depth of grind will still leave the widths of the lands within the required tolerances and of such character that each spring portion best serves its required function.

From the foregoing, it will be observed that within limits and permissible quantity production tolerances, many varying factors may be controlled. With the prescribed width and depth of the body portion of the wire section such as may be required to provide the desired tensile and/or compressive strength, (a) variations in diameter of the coils can be accurately controlled, (b) the spring may be ground to the proper diameter or diameters of clutch surface, and (c) the width or gradiently varying widths of the land may be held and controlled within practicable, permis sible tolerances.

We claim:

1. A tubular clutch spring formed of a series of wire coils fashioned to provide a clutch surface of substantially cylindrical form, the wire of which the coils are formed being approximately six sided and having its greater width nearer the clutch surface than the opposite surface, the cross section of the wire in the portion thereof between the line defining its greatest width and a line defining its clutch surface being in the form of a regular trapezoid and the cross section of the wire in the portion thereof between the said line and the line defining said opposite surface being substantially rectangular.

2. A clutch spring of tubular form comprising a series of coils, said spring having load carrying coils at one end and energizing coils at the other, said spring being formed at the clutching periphery with gradiently increased diameter and gradiently decreasing clutching land surface width in a directon from the load carrying end of the spring toward the energizing end.

3. As an article of manufacture, a clutch spring of tubular form comprising a series of coils wound from stock of uniform cross section to maintain a uniform helix, said spring having a load carrying end and an energizing end, each coil having a clutching surface lying between side wall surface portions of the stock which converge at a relatively wide angle toward the clutching surface, said clutching surface or part thereof having substantially cylindrical clutching lands which gradiently increase in width in a direction from the energizing end of said spring toward the load carrying end thereof.

4. A clutch spring of tubular form comprising a series of coils, said spring having a load carrying end and an energizing end, each of said coils being formed with a clutching land surface, the portions of the coils bearing the clutching land surface being spaced apart to form a helical channel surrounding the spring, said channel gradiently increasing in depth radially of the coils and the clutching land surface gradiently decreasing in width axially of the coils in a direction from the load carrying toward the energizing end of said spring.

5. A clutch spring of tubular form comprising end and an energizing end, one peripheral face portion of the spring forming a clutching surface with successive turns spaced apart axially of the spring to provide a helical channel thereabout, the side portions of said coils extending approximately in face to face engagement, the clutching face portions of the coils gradiently increasing in diameter and decreasing in width in a direction from the load carrying end of said spring toward the energizing end thereof, and the radial depth of the channel gradiently increasing in said direction.

6. As an article of manufacture, a spring clutch element comprising a, coiled, drawn or rolled, wire having mutually adjacent approximately parallel side faces and oppositely disposed converging side faces adjacent the peripherally exposed portion of the element which is to serve as the clutching surface portion, the wire, as drawn or rolled, having a cross sectional dimension radially of the coil greater than the cross sectional dimension axially of the coil, and having a relatively narrow clutching-land surface as compared to the radial breadth of the mutually adjacent face surfaces and the maximum axial dimension of the individual coils, which clutching-land surface increases in width toward one end of the coil.

'7. As an article of manufacture, a coiled, drawn or rolled wire adapted to serve as a friction clutch element, the wire as formed and coiled having a greater cross sectional dimension radially of the a series of coils, the spring having a load carrying coils than axially thereof, the coils having ap-- proximately parallel mutually adjacent faces, radially exposed intermediate approximately cylindrical non-clutching faces and radially exposed intermediate clutching faces opposite the non-clutching faces, said clutching faces being materially narrower axially of the coils than the mutually adjacent and non-clutching faces.

8. The article according to claim 7 wherein the clutching faces vary in width axially of the coils to provide larger clutching land area per lineal unit of wire toward the end of the clutch element which, in operation of the clutch, transmits greater clutching pressure per unit of clutch engaging surface.

9. As an article of manufacture, a coiled clutch spring element wound from wire stock of uniform section having paired side faces which converge slightly and adjacent narrower paired side faces which converge at a considerably wider angle, the slightly converging side faces becoming approximately parallel and mutually adjacent to each other in the wound spring, and wherein a clutch-engaging surface is formed On each coil lying between the widely divergent sides, the clutch-engaging surface being narrow as compared to the mutually adjacent coil faces and to the average dimension of the stock axially of the coils, said clutch-engaging surface gradiently increasing in width, axially of the coils in a direction from one end of the element toward the other.

10. As an article of manufacture, a spring clutch element comprising a coiled, drawn or rolled wire of bi-symmetrical elongated generally hexagonal form, the coils having mutually adjacent approximately parallel faces, and converging faces connected by a clutching face which is narrower axially of the coil than the nonclutching face lying radially opposite the clutching face and narrower than the mutually adjacent faces of adjacent coils.

11. A helical torque-transmitting member whereof the individual coils of the wire from 9 which the member is made are uniformly of keystone section by reason of having somewhat non-parallel main sides and having, in addition, paired approximately straight sides converging at a, relatively wide angle as compared to the 5 keystone-forming sides and being connected by a curved surface portion peripherally of the member, the approximate center of the curve lying between said wide angle sides and beyond the region which is situated between the keystoneforming sides in a direction toward the midpoint of the curve.

WILLIAM CARLEFION STARKEY.

HAMILTON L. MCCORMICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,043,695 Brownlee June 9, 1936 2,052,961 Bonham Sept. 1, 1936' 2,336,757 Starkey Dec. 14, 1943 

